Sketch is a small, simple system for producing line drawings of two- or three-dimensional solid objects and scenes. It began as a way to make illustrations for a textbook after we could find no suitable tool for this purpose. Existing scene processors emphasized GUIs and/or photo-realism, both un-useful to us. We wanted to produce finely wrought, mathematically-based illustrations with no extraneous detail. The input language is reminiscent of PSTricks, so will be easy to learn for current PSTricks users.